Paper III: Occupational Medicine 60(1), Goplen, F. K.; Grønning, M.; Aasen, N.; Nordahl, S. H., Vestibular effects of diving—a 6-year prospective study, pp. 43-48. Copyright The Author 2009. Published by Oxford University Press on behalf of the Society of Occupational Medicine. Full text not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.1093/occmed/kqp148

Abstract:

Diving has profound effects on the human body including the inner ear, which
contains the organs of hearing and balance. Ear injury is the most common medical
problem in diving. The aim of this work was to explore the short and long-term
effects of diving on hearing and balance through a simulated deep saturation dive and
two epidemiological studies on commercial divers.
The first study explored short-term effects of absolute pressure on the body. The
high-pressure neurological syndrome (HPNS) occurs at pressures exceeding 150
msw. The symptoms include tremors, decreased psychomotor performance, dizziness,
nausea and drowsiness, and there is a tendency for adaptation, since many of the
symptoms disappear quickly when pressure is held constant. In this study we
measured postural stability in a simulated saturation dive in helium-oxygen to 240
msw, which lasted for 19 days. Eight subjects participated. Postural balance was
measured 152 times during the dive by means of a force platform (static
posturography). In spite of a long compression phase (>20 h) including three stops for
adaptation, postural instability was observed throughout the bottom phase. There was
no significant adaptation, but balance normalized during the decompression. Postural
instability therefore seems to be related not only to compression rate, but also to
absolute pressure. This could indicate that posturography is more sensitive than other
methods in detecting HPNS.
The second study included 230 offshore divers who had been working on the
Norwegian continental shelf before 1990. Most of them had retired from diving. The
main finding was that these divers had more vestibular symptoms, such as dizziness,
vertigo and disequilibrium than age-matched controls, and that they also had more
postural instability as measured by static posturography. The finding is important,
since these symptoms often lead to decreased quality of life. The symptoms were
strongly associated with a previous history of decompression sickness, which is one
of the major causes of morbidity in professional divers. The third study included 67 young subjects attending a basic course for professional
divers. They were examined at the course, after three and six years. Transient
dizziness or vertigo was a common experience while diving, and the possible causes
are discussed in this thesis. We found no long-term effects of frequent diving per se
on balance or subjective disequilibrium. There were no cases of inner ear barotrauma
or inner ear decompression sickness during follow-up. However, there was a
progressive deterioration of hearing thresholds at 4 kHz, a frequency commonly
affected by noise. There was also an increase in the prevalence of subjective hearing
difficulties. Both were associated with occupational noise exposure, but not
significantly with the amount of diving. We therefore concluded that noise was the
most important cause of hearing loss in this diver group.
Summing up the results from the three studies, long-term effects were found on both
hearing and balance, which were associated with noise and decompression sickness
respectively. No long-term effects were found in association with frequent diving per
se, however transient postural instability appears to be a feature of deep diving, and
was found to last through the bottom phase even after a slow compression.